When we round a number the new rounded number is simpler but the value is kept close to what it was. The common method for rounding numbers is the following: we decide which is the last digit to keep and leave this digit the same the same if the next digit is less than 5 or increase it by 1 if the next digit is bigger than 5.
Because the next digit matter, it is not possible for a 5 digit number to be rounded to 6 digit number.